The present invention relates generally to special feature systems for an electronic private automatic branch exchange and more particularly to a trunk transfer feature for an electronic private automatic branch exchange which is built around a space divided solid state matrix.
Electronic private automatic branch exchanges are known in the art to provide circuitry for establishing audio paths between PABX stations or between central office trunks and PABX stations. these connections are usually accomplished through the use of a common control which directs the path finding and supervisory functions of a space divided crosspoint matrix on which the PABX station lines and central office trunk circuits appear. Normally, once a path is found between two appearances of the matrix, a sleeve lead is energized to hold the crosspoints of the matrix establishing the connection.
In addition to the normal control of connections between two PABX stations or a central office trunk and a PABX station, it is desirable in private automatic branch exchanges to provide certain special features to add to the flexibility of the exchange and provide additional enhancements desired by the customers. One such special feature that is useful and has gained customer acceptance in many PABX applications is that of trunk transfer.
The trunk transfer feature allows a PABX station (hereinafter called the "transferring station") which is connected to an established incoming or outgoing trunk call (hereinafter called the "transferred party") to hold the connection to the transferred party while signaling the common control to establish a connection to a transferred-to PABX station (hereinafter called the "transferree station") and then to connect the transferred party to the transferree PABX station. Thus, an incoming trunk caller reaching the wrong PABX station or wishing to talk with an individual at another PABX station after a first connection to a local station may be transferred to the desired transferee PABX station without having to redial. Similarly, a party connected to the PABX via an outgoing trunk may wich to talk to another PABX station after the first connection is completed and may be transferred without dialing.
In the past, many private automatic branch exchanges have provided the trunk transfer feature by including additional circuitry in the trunk design. Each turnk then contains transfer circuitry which permits the trunk connection (transferred party) to be held while the transferee party is being found and connected. As the number of trunks in a system increases this prior art technique increases the cost of providing the transfer feature. Not only is such a system unduly expensive, but it is also inefficient since the only transfer circuitry that is utilized during the trunk transfer is that associated with a particular trunk. Thus, much of the transfer circuitry remains unused a substantial portion of the time.
In other prior systems, transfer circuits are provided which may be accessed on a common basis through a service matrix. This access to common transfer circuitry is generally less expensive and more efficient than including transfer circuitry on individual trunks. However, certain portions of the transfer circuitry still are included on individual trunk circuits in order to access the common control for connection through the service matrix. Also, the access through the service matrix makes the trunk transfer feature traffic dependent in that an increase in the number of trunks decreases the probability of being able to access the common transfer circuitry.
Further, both of the above prior art transfer methods usually require a sleeve lead to be energized throughout the transfer process as any break in the sleeve circuit will drop the path found between marked matrix appearances.
Recently, an electronic private automatic branch exchange which is built around a space divided rectangular solid state switching matrix was developed to provide an exchange which is more dependable in operation and less subject to misoperation due to interference, cross-talk and other problems.
In this exchange one side of the solid state matrix provides line appearances which are connected to line circuits, tone receivers, senders and operator loops. The other coordinate side of the matrix provides junctor appearances for connection to an attendant junctor, local junctor and trunk junctors. The solid state switching matrix is a single stage matrix providing direct connection between line appearances and junctor appearances by the closing of a single crosspoint, and connection between lines within the system is effected simply by the interconnection of a pair of crosspoints associated with the respective lines and a selected junctor, thereby providing a greatly decreased amount of switching for establishing a connection through the matrix.
The electronic private automatic branch exchange providing the above features is more fully described in copending application, entitled, "Electronic Private Automatic Branch Exchange", Ser. No. 431,928, filed on Jan. 9, 1974, in the names of Uwe A. Pommerening and Glenn L. Richards, assigned to the same assignee as the present application, and the disclosure of which is incorporated herein by reference.
The control system for the matrix of the above-referenced exchange is more fully described in a copending application, entitled, "Matrix Control For Electronic Private Automatic Branch Exchange", Ser. No. 431,878, filed on Jan. 9, 1974, in the names of Uwe A. Pommerening and Glenn L. Richards, assigned to the same assignee as the present invention, and the disclosure of which is incorporated herein by reference.
A tone control arrangement for the above referenced exchange is more fully described in a copending application, entitled, "Tone Control For Electronic Private Automatic Branch Exchange", Ser. No. 431,885, filed on Jan. 9, 1974, in the names of Glenn L. Richards and Uwe A. Pommerening, assigned to the same assignee as the present invention, and the disclosure of which is incorporated herein by reference.